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The growth and geometric structure of ultrathin zinc oxide films on Pd(111) has been studied by scanning tunneling microscopy, low-energy electron diffraction, and density functional theory calculations. For sub-monolayer coverages, depending on the oxygen pressure, two well-ordered zinc oxide phases with (4 × 4) and (6 × 6) coincidence structures form, which are attributed to H-terminated Zn6O5 and graphite-like Zn6O6 layers, respectively. The (6 × 6) phase exhibits a pronounced oxygen pressure dependence: at low p(O2) a well-ordered (6 × 6) two-dimensional array of O vacancies develops, yielding a layer with a formal Zn25O24 stoichiometry, while at high p(O2) the Zn6O6 monolayer transforms into bilayer islands. For oxide coverages up to 4 monolayers the graphite-like Zn6O6 structure is thermodynamically the most stable phase over a large range of oxygen chemical potentials, before it converges to the bulk-type wurtzite structure. Under oxygen-poor conditions a compressed overlayer of Zn adatoms can be stabilized on top of the Zn6O6 structure.

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A scanning tunneling microscopy (STM) study, combined with density functional theory (DFT) calculations and thermal desorption spectroscopy (TDS) data, on the growth and structure of Zn on a Pd(111) surface is presented. The STM results demonstrate that PdZn(111) surface alloy bilayer islands with a p(2 × 1) structure already form during the room temperature deposition of submonolayer amounts of Zn on Pd(111). DFT calculations predict that the PdZn bilayers are energetically more stable than single PdZn layers and establish their structural parameters. The TDS data show that Zn desorbs below 600 K in a multiple-peak desorption structure with fractional order desorption kinetics of the individual components, which is due to multilayer Zn desorption. The experimentally derived adsorption energies of the low temperature desorption peaks are reproduced in the DFT calculations. At temperatures above 750 K, Zn desorbs from the PdZn alloy, and the desorption kinetics is a mixture of a first-order and a diffusion-limited desorption process.

The adsorption of carbon monoxide on Rh(111) and on oxygen modified Rh(111) was investigated using thermal desorption spectroscopy, reflection absorption infrared spectroscopy (RAIRS), and density functional theory. The results show that CO adsorbs on Rh(111) in on top sites at low coverages. With increasing coverage hollow sites and bridge sites get occupied according to the RAIRS results. A new vibrational feature at high wave numbers was found in the on top region of the CO stretching frequency. This feature can be explained by a local high density CO structure where two CO molecules are adsorbed in the ( radical3x radical3)R30 degrees structure. The coadsorption of oxygen and carbon monoxide leads to a shift of the CO stretching frequency to higher wave numbers with increasing O to CO ratio. CO adsorption on a (2x1) oxygen layer is possible and RAIRS shows that the CO adsorbs in on top and most likely in bridge sites in this case.